In a communication system, such as a wireless communication system, devices may communicate with one another via a wireless communication link. For example, a wireless station and user equipment (UE) may communicate via wireless channels. A fundamental aspect to maintaining this communication link is link adaptation. For example, the wireless station communicates to the UE in a manner tailored to the channel conditions experienced by the UE. The wireless station is able to perform link adaptation based on receiving one or more channel quality indicators (CQIs) from the UE. For example, the UE may transmit a CQI report that includes one or more CQIs. The UE generates the CQI(s) based on its estimation of existing channel conditions. CQIs may also provide a basis for adapting other communicative operations, such as scheduling, etc.
In wideband communication systems (e.g., employing orthogonal frequency-division multiplexing (OFDM)), the bandwidth may be divided into several sub-bands, where each sub-band covers a number frequency units (e.g., sub-carriers in OFDM). In such a communication system, wideband CQI(s) may cover the whole bandwidth or a part of the whole bandwidth (e.g., one or more sub-bands). Based on this framework, when the frequency domain granularity of the CQI is narrow, the performance of link adaptation, scheduling, and other communicative operations (e.g., power control, timing control, handover, beamforming, etc.) may be improved compared to when the frequency domain granularity of the CQI is broader.
Problems exist, however, when implementing a narrower frequency domain granularity for CQI(s). For example, this typically results in more overhead. This is especially true in time division duplex (TDD) communication systems (e.g., long term evolution LTE-TDD or Worldwide Interoperability for Microwave Access (WiMax)) because of the asymmetric allocation of uplink and downlink timeslots. For example, where a high asymmetry exists (e.g., DL to UL is 9:1) and/or heavy data traffic exists, an UL CQI report channel may support only wideband CQI (e.g., the whole bandwidth or sub-band CQI(s) having a coarse frequency domain granularity). Another problem is that when the frequency domain granularity of the CQI(s) is narrow, the wireless station may take a longer period of time to update and/or adapt. As a result, the performance of the wireless station with respect to link adaptation, scheduling, and/or other communicative operations may be degraded.
While the existence of channel reciprocity in TDD communication systems is well known, channel reciprocity does not resolve all the issues related to link adaption, scheduling, and other communicative operations. For example, in a TDD communication system, the interference between uplink and downlink directions does not necessarily correlate at all (i.e., interference is not reciprocal).